690 OLIGOCHAETA 



(a) The clitellar setae are usually modified in both families, being longer than 

 those upon the non-clitellar segments. 



(3) The spermathecae are without diverticula. 



(4) There are no spermiducal glands in the Lumbricidae, and these structures 



are absent in a large number of Geoscolicidae. 



(5) The supra-intestinal blood-vessel is wanting in the Lumbricidae, and in 



many, if not most, Geoscolicidae. 



Besides these general facts of resemblance, which point to an affinity between the 

 two groups, there are a few points of similarity shown by individual genera and 

 species. Thus KosA has pointed out that in A. coviplanata, the commencement of 

 the large intestine is sacculated, as it is in certain Geoscohcidae, for example Hormo- 

 gaster. The last-named genus also approaches the Lumbricidae, in that the male 

 pores are situated between segments xv/xvi. In. another Geoscolicid, viz. Kynotus 

 michaelseni, the male pores are actually upon the fifteenth segment. 



It should be perhaps remarked that the invariably paired character of the nephridia 

 is another bond of union between the Lumbricidae and the Geoscolicidae. 



The Lumbricidae are found in nearly every part of the world. But they are 

 most characteristic of the Palaearctic and Nearctic regions of Sclatee. In fact, they 

 practically constitute the earthworm fauna of these regions, but few additional types 

 being found. An important question is — How far are they really indigenous to 

 tropical countries ? I have entered into this question already (p. 149) more fully, but 

 a few points may be noted here. 



The most striking fact in favour of considering the Lumbricidae to be indigenous 

 to Europe, Asia, and North America, and to have been introduced accidentally else- 

 where is the invariable identity of Lumbricidae met with outside those two regions 

 with forms well known from Europe, North Asia, and North America. If 

 different species were found, for example in New Zealand, the possibility of the 

 Lumbricidae being a genuine case of a widely distributed family would have to be 

 reconsidered. 



The genus Lumbricus of older authors was divided by Eisen into the two 

 genera Lumbricus and Allolobophora ; they are thus defined by him: — 



Lumbricus (s. s). — ' Tubercula ventralia in segmento 14. Setae ubique binae approxi- 

 matae. Lobus cephalicus postice segmentum buccale in duas partes 

 dividens.' 



Allolobophora. — 'Tubercula ventralia in segmento 14. Setae ubique binae approxi- 

 matae. Lobus cephalicus postice segmentum buccale non dividens.' 



